1. Field of the Invention
The invention relates to a brushless DC motor drive system for driving a fan, blower and so forth, and a method of driving the brushless DC motor.
2. Description of the Related Art
With a brushless DC motor for driving a fan and blower, there has lately been an increase in demand for high power and variable speed, and a variable speed range is required to have a wide scope ranging from high-speed to low-speed.
With the conventional brushless DC motor drive system, for controlling a duty angle, a rotational speed of a brushless DC motor is varied by adjusting a time length from a point in time when an induced voltage is turned from zero up to a point in time when an energization signal is turned ON, and by turning the energization signal OFF when the induced voltage is turned to zero again.
With the brushless DC motor drive system as described, however, the same has drawbacks in that because the energization signal is turned ON in a region where the induced voltage drops, the brushless DC motor is poor in efficiency and further, its vibration is large.